The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
During integrated circuit (IC) manufacturing, transistors are fabricated and then connected together to perform desired circuit functions. The connection process is generally called “metallization” and is usually performed using patterning, etching, and deposition steps.
Tungsten (W) may be used to provide low resistance electrical connections in trenches, vias or contacts. When depositing W, titanium nitride (TiN) is often used as a barrier layer between the W and underlying layers. W may be deposited through the reduction of tungsten hexafluoride (WF6) by molecular hydrogen (H2) or silane (SiH4). However, fluorine-based precursor gases may not be compatible with certain processes. Fluorine-free processes may also be used to deposit W using thermal atomic layer deposition (ALD). However, thermal ALD of W using fluorine-free precursor gas may cause etching of the TiN barrier layer.
ALD is a cyclic process that may be used to deposit W on a substrate by sequentially exposing the substrate in a processing chamber to a precursor gas that is adsorbed onto a surface of the substrate. The processing chamber is purged, exposed to a reactant gas to cause a chemical reaction with the adsorbed precursor, and then purged again. The cycle is repeated multiple times. Heat is used to promote the reaction.
When depositing W, growth enhancers (such as BHx polymer, SiHx, . . . ) may be used before the thermal ALD deposition of the W. In addition, a W nucleation layer may be formed by ALD of W precursor with a reducing agent such as SiH4, diborane (B2H6) or germane (GeH4). However, the growth enhancers and nucleation layers tend to increase the resistivity of the W.